Etiology and antimicrobial susceptibility profiles of anaerobic bacteria isolated from clinical samples in a university hospital in Madrid, Spain.

Abstract Background The anaerobic infection management is usually based on empirical treatment because anaerobic culture techniques take a long time due to their fastidious nature. The aim of this study was to analyze the etiological profile of severe anaerobic infections and AST data from clinical anaerobic bacteria isolated in a tertiary hospital in Madrid (Spain). Material and methods A consecutive study was carried out over 19 months in Ramon y Cajal Universitary Hospital, Madrid. Clinical samples were processed in appropriate anaerobic media and incubated using Anoxomat system. Identification was performed by MALDI-TOF. AST were determined with gradient diffusion method using EUCAST (penicillin, co-amoxiclav, imipenem, clindamycine and metronidazole) or CLSI (cefoxitin) breakpoints. Results During the period of study, 503 anaerobic microorganisms isolated from 424 clinical samples were included. Twenty-six percent of the cultures were monomicrobial, while 70.0% also contained aerobic bacteria. The most common source of infection was abscesses (26%), while blood infections represented the 11%. Anaerobic gram-negative bacilli were predominant (41%), being Bacteroides fragilis (13%) the most prevalent overall; anaerobic gram-positive bacilli represented 35%, anaerobic gram-positive cocci 19% and anaerobic gram-negative cocci 5%. Metronidazole and imipenem were the most effective agents tested against anaerobic bacteria, while clindamycin presented higher resistance rates. Conclusion Antimicrobial susceptibility surveillance of anaerobic bacteria should be performed to monitor changes in resistance patterns and to be able to optimize empiric antimicrobial treatment. Reliable species identification and quick reporting of results would guide clinicians to select the optimal antimicrobial therapy.